Air fuel ratio distribution to enhance gasoline engine operation

ABSTRACT

A silicone is added in a minor proportion to a nonleaded gasoline to improve the distribution of the air-fuel mixture in the induction system of an aspirated multicylinder gasoline engine, thereby increasing operating efficiency.

United States Patent 11 1 Zimmerman et a1.

1 1 Oct. 2, 1973 I 1 AIR-FUEL RATIO DISTRIBUTION TO ENHANCE GASOLINE ENGINE OPERATION [75 Inventors: Abraham A. Zimmerman, New

Providence; Louis E. Furlong, Westfield; Hugh F. Shannon, Scotch Plains, all of NJ.

[73 J Assignee: Esso Research and Engineering Company, Linden, NJ. 221 Filed: Nov. 16, 1971 211 App]. No.: 199,303

UNITED STATES PATENTS 2,986,874 6/1961 George 44/76 2,862,885 12/1958 Nelson et a1 44/76 2,432,109 12/1947 Zisman ct a1, .1 44/76 2,765,221 10/1956 Lusenbrink et a1 44/76 Primary Examiner-Daniel E. Wyman AssistantExaminerMrs. Y. H. Smith Attorney-Leon Chasan et a1.

[57] ABSTRACT A silicone is added in a minor proportion to a nonleaded gasoline to improve the distribution of the airfuel mixture in the induction system of an aspirated multicylinder gasoline engine, thereby increasing operating efficiency.

4 Claims, No Drawings AIR-FUEL RATIO DISTRIBUTION TO ENHANCE GASOLINE ENGINE OPERATION BACKGROUND OF THE INVENTION This invention concerns an improved motor fuel composition and an improved method of operating an internal combustion engine. More particularly, the invention concerns incorporating into a motor fuel, such as gasoline, an additive combination that will modify the induction tract surfaces of an aspirated multicylinder'internal combustion engine in such a way as to improve the geometric and time distribution of the fuel in the induction system of that engine.

In operating a gasoline engine, it is necessary to supply to the cylinders a mixture of gasoline and air in proper proportions. In most instances, this is accom-' plished by the use of a carburetor wherein the fuel is aspirated into a stream of moving air. In an aspirated multicylinder engine the mixture of air and fuel is dis tributed to the various cylinders through an intake manifold. One problem that arises in such a system is that the air/fuel ratio tends to vary from cylinder to cylinder, i.e., there is a geometric variation, some cylinders receiving a relatively rich mixture and others a relatively lean mixture. Similarly, variations in air/fuel ratio in particular cylinders of a multicylinder engine can vary with respect to time. Such variations cause an engine to accelerate and decelerate as frequently as once per second, even though an attempt is made to hold the vehicle under steady cruise conditions with a fixed position of the throttle. If the variation in air/fuel ratio with time becomes sufficiently severe, it feels to the automobile driver as if his car is being buffeted by winds.

Both the geometric variation in air/fuel ratio distribution and the variation with respect to time result in reduced operating efficiency, which shows up in at least two ways, one being a loss in fuel economy and another being uneven and reduced power. Accordingly, it is desirable to reduce such variations.

Gasolines used as motor fuels comprise a mixture of hydrocarbons of various boiling points. Thus, a gasoline can have an initial boiling point in the range of about 250 to 450F., at atmospheric pressure. The mixture of gasoline and air that leaves the carburetor and passes to the various cylinders through the intake manifold tends to deposit some of the higher boiling fractions in the form of a liquid film on the walls of the intake manifold. This liquid film is the main factor in poor fuel distribution in the engine. Accordingly, it is desirable to have the gasoline present as a vapor or spray in the air/fuel mixture to ensure greater engine operating efficiency.

DESCRIPTION OF THE INVENTION sults from a phenomenon wherein at least a portion of the additive becomes adsorbed on the walls of the intake system of the engine to create a surface which is not easily wetted by liquid drops of of gasoline. Thus,

any drops of gasoline that fall out of the mixture of gasoline and air in the intake system, do not spread into. a film but remain as discrete drops so that they are more easily reentrained in the air stream passing through the manifold.

The silicones that are used in this invention can be further characterized as compounds of the formula:

wherein n is a whole number of at least 2 and wherein at least one R attached to each silicon atom is methyl and each remaining R is straight chain or branched chain, preferably straight chain, C to C, alkyl, or a straight chain or branched chain, preferably straight chain, C to C alkyl group wherein at least two hydrogen atoms have been replaced by fluorine, thus providing at least one CI} or CF H group on the chain. The fluorinated alkyl group can be fully fluorinated, if desired, i.e., it can be a perfluoroalkyl group. R' in the above formula can be any terminating group, as is known in the silicone art. Thus, one R could be hydrogen or methyl and the other one could be an OH group, a CH group, for example. Very often in silicone designation the R groups are not definitely characterized, as impurities in the reaction mix can also act as terminating groups.

The viscosities of the silicones used in this invention will be within therange of 5 to 8,000 centistokes, preferably 20 to 5,000 centistokes, measured at 25C. Silicones of higher viscosity than about 8,000 centistokes at 25C. are not desirable because of their tendency to cause spark plug deposits as well as to form deposits on the undersides of the intake valves of an internal combustion engine.

It is known to add silicones to gasoline, as taught, for example, in US. Pat. No. 2,529,496, for the purpose of preventing an increase in the octane demand of an internal combustion engine on prolonged operation. The gasoline to which the invention in that patent was directed contained tetraethyl leadl. One finding of the present invention is that when silicones are added to a gasoline there is an improvement in the distribution of the air/fuel mixture to the various cylinders of the gasoline engine, thus improving the smoothness of operation. However, if the silicone is added to a gasoline that also contains a lead antiknock additive there is an adverse effect on the valves of that engine. It is a further finding of the present invention that silicones when added to a nonleaded gasoline will improve the air/fuel mixture distribution with no adverse effects on the operation of the engine.

The silicone compounds of the present invention will be incorporated into a nonleaded gasoline composition in an amount ranging from about 2 to 50 pounds, or more usually from about 5 to 20 pounds, of the silicone per thousand barrels of gasoline, one barrel of gasoline containing 42 US. gallons. A concentration of 1 pound per thousand barrels of gasoline is roughly equal to about 4 parts per million; thus, a. range of from 2 to 50 pounds per thousand barrels is roughly equal to a weight percent concentration of from about 0.0008 to about 0.02 weight percent.

The substituted and unsubstituted silicones that will be used in this invention include dimethyl silicone, methyl n-decyl silicone, methyl octadecyl silicone, methyl isobutyl silicone, methyl dodecyl silicone, methyl perfluoropropyl silicone, and methyl trifluoro tetradecyl silicone.

The gasolines in which the additives of this invention are employed are conventional petroleum distillate fuels boiling in the gasoline range and intended for internal combustion engines, preferably spark ignition engines. Gasoline is defined as a mixture of liquid hydrocarbons having an initial boiling point somewhere in the range of about 70 to 135F. and a final boiling point somewhere in the range of about 250 to 450F. Gasolines are supplied in a number of different grades, depending upon the type of service for which they are intended. The additives of the invention are particularly useful in motor and aviation gasolines. Motor gasolines include those defined by ASTM Specification D- 439-58T, Types A, B and C, and are composed of a mixture of various types of hydrocarbons, including aromatics, olefins, paraffins, isoparaffins, naphthenes, and, occasionally diolefins. Not all of these types of hydrocarbons will necessarily be present in any particular gasoline. These fuels are derived from petroleum crude oil by various refining processes, including fractional distillation, catalytic cracking, hydroforming, alkylation, isomerization, polymerization and solvent extraction. Motor gasolines normally have boiling ranges within the limits of about 70F. and about 450F., while aviation gasolines have narrower boiling ranges, within the limits of about 100F. and 330F. The vapor pressures of gasoline as determined by ASTM Method D-323 vary between about 5 and about 18 psi. at 100F. The properties of aviation gasolines are set forth in U.S. Military Specification MlL-F-5572 and ASTM Specification D-9l0-57T.

The additives employed in accordance with this invention can be used in gasolines with other additive agents conventionally used in such fuels. These include corrosion inhibitors, rust inhibitors, antioxidants, solvent oils, antistatic agents, dyes, anti-icing agents, e.g., isopropanol, hexylene glycol, and the like. There may also be included certain oil-soluble dispersants and detergents to provide significant improvement in overall engine cleanliness. This is taught, for example, by Calvino et al. in U.S. Pat. No. 3,223,495.

The nature of this invention and the advantages accruing from the practice thereof will be better understood when reference is made to the following examples, which include a preferred embodiment.

EXAMPLES A gasoline blend was prepared using as the base an unleaded gasoline of 97 Research Octane rating that had an initial boiling point of 97F, a 50 percent boiling point of 230F., and a final boiling point of 386F., by ASTM Distillation Method D-86. The gasoline blend was prepared by adding to the gasoline, by simple mixing, a dimethyl silicone at a concentration of 20 pounds per thousand barrels of gasoline. The dimethyl silicone had a viscosity of 350 centistokes at 25C. The gasoline blend was then used as the fuel to operate a one-cylinder Wisconsin gasoline engine which was run at 1800 rpm for 14 hours. The Wisconsin engine is an L-head engine in which the fuel is mixed with air in a carburetor. The engine was equipped with a removable intake unit. During the test, the temperature of the air/fuel mixture in the intake unit and the temperature of the intake air were controlled at F. and F. respectively so as to simulate typical intake conditions. From previous experience it was found that a 14-hour test period was sufficient to enable the additive in the gasoline to reach equilibrium adsorption levels on the intake surfaces. At the end of the test, the intake unit was removed from the engine and tested for nonwetting properties. The test consisted in placing six separate drops of gasoline on different areas of the intake unit surface and then measuring the average diameter of the area over which the gasoline spread on the surface. A similar test was run on an intake unit from the Wisconsin engine test in which no additive had been incorporated in the base gasoline. In each instance the diameter was measured to the nearest one-quarter inch. The results were as follows TABLE I Diameter Spread, Inches No additive 2 20 ptb of silicone It will be seen that in the case of the test wherein the engine had been run with the gasoline containing the silicone, the intake surfaces had been rendered more resistant to wetting by gasoline than had the intake surfaces of the engine run with the gasoline containing no added silicone. Based on a large number of tests, it has been determined that there is a good correlation between the results of the above-described Wisconsin engine test and a tendency for car hesitation on acceleration under actual driving conditions. When there is wide spread between the air/fuel ratios of the mixture reaching the several cylinders of an automotive engine and/or when there is a wide variation of air/fuel ratio with respect to time for particular cylinders, there will be a tendency for hesitation or even actual stalling when attempting to enter a stream of fast-moving traffic from a side street. This is shown by the following test results.

A 1970 Chevrolet eight-cylinder automobile was chosen for the test. The car was first run until it had warmed up to normal operating temperatures. It was then accelerated from a standing position to high driving speed as rapidly as possible and any tendency for hesitation was noted. In all of the test runs the same driver was used, accompanied by two additional observers, who were always the same persons. The car was first tested with the non-leaded gasoline of about 97 research octane rating described above. The car was then tested with a gasoline blend prepared by adding to a portion of that same gasoline dimethyl silicon at the concentration of 10 pounds per thousand barrels; the dimethyl silicone had a viscosity of 350 centistokes at 25C.

The tendency for hesitation on acceleration was noted by the driver and the two other observers and there was some variation the test was run as many as times and the most consistent ratings were chosen.

The test results are shown in Table [1, which follows TABLE II Fuel Hesitation Merit Rating Non-leaded gasoline l.52.0 Non-leaded gasoline 10 ptb silicone 4 It is seen that incorporation of the dimethyl silicone into the gasoline considerably reduced the hesitation tendency.

Evidence of the lack of any operating problem when employing a silicone in a non-leaded gasoline is found in the results of tests run in a six-cylinder Ford engine. The engine was mounted on a test stand and was run for a total of 110 hours in a cyclic operation wherein for 1% hours the engine was idled at a 13/1 air/fuel ratio and then for 4 hours the engine was run at 2,000 rpm with a 14/1 air/fuel ratio under a load of 105 ft. pounds. In one test the engine was operated with a leaded gasoline containing 3 cc of tetraethyl lead per gallon as well as dimethyl silicone of 350 centistokes viscosity (at 25C.) which had been added to the gaso line at the rate of 20 pounds per thousand barrels. At the end of the test, after shutdown while the engine was still warm, the compression pressures on each cylinder were measured using standard procedures. It was found that two of the cylinders had lost considerable compression, the readings in cylinder number order being 185, 187, 165, 180-, 190 and 198 psig, as compared withnormal readings in the range of 193 to 198. Moreover, when the exhaust valves were removed from the engine and inspected, two of them showed clearly visible channels and indentations on their faces, this being indicative of blowby. A similar run made with a nonleaded gasoline containing the same silicone at a concentration of 20 pounds per thousand barrels gave no r 6 evidence of blowby or loss of compression.

As an added example of the invention, methyl perfluoro propyl silicone is added to a non-leaded gasoline of about research octane number, at the rate of about 12 pounds per thousand barrels.

The specific examples herein presented are not intended to limit the scope of this invention in any man ner. The scope is to be determined by the appended claims.

What is claimed is:

l. A gasoline composition comprising a major proportion of a non-leaded gasoline into which has been incorporated from about 2 to about 50 pounds, per thousand barrels of gasoline, of a silicone having a viscosity of from 5 to 8,000 centistokes at 25C., said silicone being represented by the formula:

If R

wherein n is a whole number of at least 2 and wherein at least one R attached to each silicon atom is methyl and each remaining R is C to C alkyl, or C to C alkyl wherein at least two hydrogen atoms have been replaced by fluorine, thus providing at least one CF or CF H group on the chain, R' being a terminating group.

2. Composition as defined by claim 1 wherein said silicone is dimethyl silicone.

3. Composition as defined by claim 1 wherein said silicone is methyl perfluoropropyl silicone.

4. The method of improving the operation of an internal cmbustion engine which comprises running said engine with the non-leaded gasoline composition of claim 1. 

2. Composition as defined by claim 1 wherein said silicone is dimethyl silicone.
 3. Composition as defined by claim 1 wherein said silicone is methyl perfluoropropyl silicone.
 4. The method of improving the operation of an internal cmbustion engine which comprises running said engine with the non-leaded gasoline composition of claim
 1. 